Processes for the production of electro-optic displays

ABSTRACT

Electrical connection between the backplane and the front electrode of an electro-optic display is provided by forming a front plane laminate ( 100 ) comprising, in order, a light-transmissive electrically-conductive layer ( 104 ), a layer of electro-optic material ( 106 ), and a layer of lamination adhesive ( 108 ); forming an aperture ( 114 ) through all three layers of the front plane laminate ( 100 ); and introducing a flowable, electrically-conductive material ( 118 ) into the aperture ( 114 ), the flowable, electrically-conductive material being in electrical contact with the light-transmissive electrically-conductive layer ( 104 ) and extending through the adhesive layer ( 108 ).

REFERENCE TO RELATED APPLICATIONS

This application claims benefit of copending Application Ser. No.61/676,356, filed Jul. 27, 2013.

This application is also related to:

(a) U.S. Pat. Nos. 6,982,178; 7,236.292; 7,443,571; 7,729,039;8,068,272; and 8,077,381;

(b) U.S. Pat. No. 7,733,554;

(c) U.S. Pat. No. 7,910,175;

(d) U.S. Pat. No. 7,583,427; and

(e) U.S. Pat. Nos. 7,843,624; 8,034,209; and 8,390,301.

The entire contents of these patents, and of all other U.S. patents andpublished and copending applications mentioned below, are hereinincorporated by reference.

BACKGROUND OF INVENTION

This invention relates to processes for the production of electro-opticdisplays. This invention is particularly, but not exclusively, intendedfor use with displays comprising encapsulated electrophoretic media.However, the invention can also make use of various other types ofelectro-optic media which can be incorporated into a mechanicallycoherent multi-layer film, such as encapsulated liquid crystal displaysand other types of electro-optic displays discussed below.

The term “electro-optic”, as applied to a material or a display, is usedherein in its conventional meaning in the imaging art to refer to amaterial having first and second display states differing in at leastone optical property, the material being changed from its first to itssecond display state by application of an electric field to thematerial. Although the optical property is typically color perceptibleto the human eye, it may be another optical property, such as opticaltransmission, reflectance, luminescence or, in the case of displaysintended for machine reading, pseudo-color in the sense of a change inreflectance of electromagnetic wavelengths outside the visible range.

The terms “bistable” and “bistability” are used herein in theirconventional meaning in the art to refer to displays comprising displayelements having first and second display states differing in at leastone optical property, and such that after any given element has beendriven, by means of an addressing pulse of finite duration, to assumeeither its first or second display state, after the addressing pulse hasterminated, that state will persist for at least several times, forexample at least four times, the minimum duration of the addressingpulse required to change the state of the display element. It is shownin U.S. Pat. No. 7,170,670 that some particle-based electrophoreticdisplays capable of gray scale are stable not only in their extremeblack and white states but also in their intermediate gray states, andthe same is true of some other types of electro-optic displays. Thistype of display is properly called “multi-stable” rather than bistable,although for convenience the term “bistable” may be used herein to coverboth bistable and multi-stable displays.

Several types of electro-optic displays are known. One type ofelectro-optic display is a rotating bichromal member type as described,for example, in U.S. Pat. Nos. 5,808,783; 5,777,782; 5,760,761;6,054,071 6,055,091; 6,097,531; 6,128,124; 6,137,467; and 6,147,791(although this type of display is often referred to as a “rotatingbichromal ball” display, the term “rotating bichromal member” ispreferred as more accurate since in some of the patents mentioned abovethe rotating members are not spherical). Such a display uses a largenumber of small bodies (typically spherical or cylindrical) which havetwo or more sections with differing optical characteristics, and aninternal dipole. These bodies are suspended within liquid-filledvacuoles within a matrix, the vacuoles being filled with liquid so thatthe bodies are free to rotate. The appearance of the display is changedby applying an electric field thereto, thus rotating the bodies tovarious positions and varying which of the sections of the bodies isseen through a viewing surface. This type of electro-optic medium istypically bistable.

Another type of electro-optic display uses an electrochromic medium, forexample an electrochromic medium in the form of a nanochromic filmcomprising an electrode formed at least in part from a semi-conductingmetal oxide and a plurality of dye molecules capable of reversible colorchange attached to the electrode; see, for example O'Regan, B., et al.,Nature 1991, 353, 737; and Wood, D., Information Display, 18(3), 24(March 2002). See also Bach, U., et al., Adv. Mater., 2002, 14(11), 845.Nanochromic films of this type are also described, for example, in U.S.Pat. Nos. 6,301,038; 6,870,657; and 6,950,220. This type of medium isalso typically bistable.

Another type of electro-optic display is an electro-wetting displaydeveloped by Philips and described in Hayes, R. A., et al., “Video-SpeedElectronic Paper Based on Electrowetting”, Nature, 425, 383-385 (2003).It is shown in U.S. Pat. No. 7,420,549 that such electro-wettingdisplays can be made bistable.

One type of electro-optic display, which has been the subject of intenseresearch and development for a number of years, is the particle-basedelectrophoretic display, in which a plurality of charged particles movethrough a fluid under the influence of an electric field.Electrophoretic displays can have attributes of good brightness andcontrast, wide viewing angles, state bistability, and low powerconsumption when compared with liquid crystal displays. Nevertheless,problems with the long-term image quality of these displays haveprevented their widespread usage. For example, particles that make upelectrophoretic displays tend to settle, resulting in inadequateservice-life for these displays.

As noted above, electrophoretic media require the presence of a fluid.In most prior art electrophoretic media, this fluid is a liquid, butelectrophoretic media can be produced using gaseous fluids; see, forexample, Kitamura, T., et al., “Electrical toner movement for electronicpaper-like display”, IDW Japan, 2001, Paper HCS1-1, and Yamaguchi, Y.,et al., “Toner display using insulative particles chargedtriboelectrically”, IDW Japan, 2001, Paper AMD4-4). See also U.S. Pat.Nos. 7,321,459 and 7,236,291. Such gas-based electrophoretic mediaappear to be susceptible to the same types of problems due to particlesettling as liquid-based electrophoretic media, when the media are usedin an orientation which permits such settling, for example in a signwhere the medium is disposed in a vertical plane. Indeed, particlesettling appears to be a more serious problem in gas-basedelectrophoretic media than in liquid-based ones, since the lowerviscosity of gaseous suspending fluids as compared with liquid onesallows more rapid settling of the electrophoretic particles.

Numerous patents and applications assigned to or in the names of theMassachusetts Institute of Technology (MIT) and E Ink Corporationdescribe various technologies used in encapsulated electrophoretic andother electro-optic media. Such encapsulated media comprise numeroussmall capsules, each of which itself comprises an internal phasecontaining electrophoretically-mobile particles in a fluid medium, and acapsule wall surrounding the internal phase. Typically, the capsules arethemselves held within a polymeric binder to form a coherent layerpositioned between two electrodes. The technologies described in thethese patents and applications include:

-   -   (a) Electrophoretic particles, fluids and fluid additives; see        for example U.S. Pat. Nos. 7,002,728 and 7,679,814;    -   (b) Capsules, binders and encapsulation processes; see for        example U.S. Pat. Nos. 6,922,276; and 7,411,719;    -   (c) Films and sub-assemblies containing electro-optic materials;        see for example U.S. Pat. Nos. 6,825,829; 6,982,178; 7,236,292;        7,443,571; 7,513,813; 7,561,324; 7,636,191; 7,649,666;        7,728,811; 7,729,039; 7,791,782; 7,839,564; 7,843,621;        7,843,624; 8,034,209; 8,068,272; 8,077,381; and 8,177,942; and        U.S. Patent Applications Publication Nos. 2008/0309350;        2009/0034057; 2009/0109519; 2009/0168067; 2011/0032595;        2011/0032396; 2011/0075248; 2011/0164301; and 2012/0176664;    -   (d) Backplanes, adhesive layers and other auxiliary layers and        methods used in displays; see for example U.S. Pat. Nos.        7,116,318; and 7,535,624;    -   (e) Color formation and color adjustment; see for example U.S.        Pat. No. 7,075,502; and U.S. Patent Application Publication No.        2007/0109219;    -   (f) Methods for driving displays; see for example U.S. Pat. Nos.        7,012,600; and 7,453,445;    -   (g) Applications of displays; see for example U.S. Pat. Nos.        7,312,784; and 8,009,348; and    -   (h) Non-electrophoretic displays, as described in U.S. Pat. Nos.        6,241,921; 6,950,220; 7,420,549 and 8,319,759; and U.S. Patent        Application Publication No. 2012/0293858.

Many of the aforementioned patents and applications recognize that thewalls surrounding the discrete microcapsules in an encapsulatedelectrophoretic medium could be replaced by a continuous phase, thusproducing a so-called polymer-dispersed electrophoretic display, inwhich the electrophoretic medium comprises a plurality of discretedroplets of an electrophoretic fluid and a continuous phase of apolymeric material, and that the discrete droplets of electrophoreticfluid within such a polymer-dispersed electrophoretic display may beregarded as capsules or microcapsules even though no discrete capsulemembrane is associated with each individual droplet; see for example,the aforementioned U.S. Pat. No. 6,866,760. Accordingly, for purposes ofthe present application, such polymer-dispersed electrophoretic mediaare regarded as sub-species of encapsulated electrophoretic media.

A related type of electrophoretic display is a so-called “microcellelectrophoretic display”. In a microcell electrophoretic display, thecharged particles and the fluid are not encapsulated withinmicrocapsules but instead are retained within a plurality of cavitiesformed within a carrier medium, typically a polymeric film. See, forexample, U.S. Pat. Nos. 6,672,921 and 6,788,449, both assigned to SipixImaging, Inc.

Although electrophoretic media are often opaque (since, for example, inmany electrophoretic media, the particles substantially blocktransmission of visible light through the display) and operate in areflective mode, many electrophoretic displays can be made to operate ina so-called “shutter mode” in which one display state is substantiallyopaque and one is light-transmissive. See, for example, U.S. Pat. Nos.5,872,552; 6,130,774; 6,144,361; 6,172,798; 6,271,823; 6,225,971; and6,184,856. Dielectrophoretic displays, which are similar toelectrophoretic displays but rely upon variations in electric fieldstrength, can operate in a similar mode; see U.S. Pat. No. 4,418,346.Other types of electro-optic displays may also be capable of operatingin shutter mode. Electro-optic media operating in shutter mode may beuseful in multi-layer structures for full color displays; in suchstructures, at least one layer adjacent the viewing surface of thedisplay operates in shutter mode to expose or conceal a second layermore distant from the viewing surface.

An encapsulated electrophoretic display typically does not suffer fromthe clustering and settling failure mode of traditional electrophoreticdevices and provides further advantages, such as the ability to print orcoat the display on a wide variety of flexible and rigid substrates.(Use of the word “printing” is intended to include all forms of printingand coating, including, but without limitation: pre-metered coatingssuch as patch die coating, slot or extrusion coating, slide or cascadecoating, curtain coating; roll coating such as knife over roll coating,forward and reverse roll coating; gravure coating; dip coating; spraycoating; meniscus coating; spin coating; brush coating; air knifecoating; silk screen printing processes; electrostatic printingprocesses; thermal printing processes; ink jet printing processes;electrophoretic deposition (See U.S. Pat. No. 7,339,715); and othersimilar techniques.) Thus, the resulting display can be flexible.Further, because the display medium can be printed (using a variety ofmethods), the display itself can be made inexpensively.

Other types of electro-optic materials may also be used in the presentinvention.

An electrophoretic display normally comprises a layer of electrophoreticmaterial and at least two other layers disposed on opposed sides of theelectrophoretic material, one of these two layers being an electrodelayer. In most such displays both the layers are electrode layers, andone or both of the electrode layers are patterned to define the pixelsof the display. For example, one electrode layer may be patterned intoelongate row electrodes and the other into elongate column electrodesrunning at right angles to the row electrodes, the pixels being definedby the intersections of the row and column electrodes. Alternatively,and more commonly, one electrode layer has the form of a singlecontinuous electrode and the other electrode layer is patterned into amatrix of pixel electrodes, each of which defines one pixel of thedisplay. In another type of electrophoretic display, which is intendedfor use with a stylus, print head or similar movable electrode separatefrom the display, only one of the layers adjacent the electrophoreticlayer comprises an electrode, the layer on the opposed side of theelectrophoretic layer typically being a protective layer intended toprevent the movable electrode damaging the electrophoretic layer.

The manufacture of a three-layer electrophoretic display normallyinvolves at least one lamination operation. For example, in several ofthe aforementioned MIT and E Ink patents and applications, there isdescribed a process for manufacturing an encapsulated electrophoreticdisplay in which an encapsulated electrophoretic medium comprisingcapsules in a binder is coated on to a flexible substrate comprisingindium-tin-oxide (ITO) or a similar conductive coating (which acts asone electrode of the final display) on a plastic film, thecapsules/binder coating being dried to form a coherent layer of theelectrophoretic medium firmly adhered to the substrate. Separately, abackplane, containing an array of pixel electrodes and an appropriatearrangement of conductors to connect the pixel electrodes to drivecircuitry, is prepared. To form the final display, the substrate havingthe capsule/binder layer thereon is laminated to the backplane using alamination adhesive. (A very similar process can be used to prepare anelectrophoretic display usable with a stylus or similar movableelectrode by replacing the backplane with a simple protective layer,such as a plastic film, over which the stylus or other movable electrodecan slide.) In one preferred form of such a process, the backplane isitself flexible and is prepared by printing the pixel electrodes andconductors on a plastic film or other flexible substrate. The obviouslamination technique for mass production of displays by this process isroll lamination using a lamination adhesive.

As discussed in the aforementioned U.S. Pat. No. 6,982,178, many of thecomponents used in solid electro-optic displays, and the methods used tomanufacture such displays, are derived from technology used in liquidcrystal displays (LCD's), which are of course also electro-opticdisplays, though using a liquid rather than a solid medium. For example,solid electro-optic displays may make use of an active matrix backplanecomprising an array of transistors or diodes and a corresponding arrayof pixel electrodes, and a “continuous” front electrode (in the sense ofan electrode which extends over multiple pixels and typically the wholedisplay) on a transparent substrate, these components being essentiallythe same as in LCD's. However, the methods used for assembling LCD'scannot be used with solid electro-optic displays. LCD's are normallyassembled by forming the backplane and front electrode on separate glasssubstrates, then adhesively securing these components together leaving asmall aperture between them, placing the resultant assembly undervacuum, and immersing the assembly in a bath of the liquid crystal, sothat the liquid crystal flows through the aperture between the backplaneand the front electrode. Finally, with the liquid crystal in place, theaperture is sealed to provide the final display.

This LCD assembly process cannot readily be transferred to solidelectro-optic displays. Because the electro-optic material is solid, itmust be present between the backplane and the front electrode beforethese two integers are secured to each other. Furthermore, in contrastto a liquid crystal material, which is simply placed between the frontelectrode and the backplane without being attached to either, a solidelectro-optic medium normally needs to be secured to both; in most casesthe solid electro-optic medium is formed on the front electrode, sincethis is generally easier than forming the medium on thecircuitry-containing backplane, and the front electrode/electro-opticmedium combination is then laminated to the backplane, typically bycovering the entire surface of the electro-optic medium with an adhesiveand laminating under heat, pressure and possibly vacuum.

Electro-optic displays are often costly; for example, the cost of thecolor LCD found in a portable computer is typically a substantialfraction of the entire cost of the computer. As the use of electro-opticdisplays spreads to devices, such as cellular telephones and personaldigital assistants (PDA's), much less costly than portable computers,there is great pressure to reduce the costs of such displays. Theability to form layers of some solid electro-optic media by printingtechniques on flexible substrates, as discussed above, opens up thepossibility of reducing the cost of electro-optic components of displaysby using mass production techniques such as roll-to-roll coating usingcommercial equipment used for the production of coated papers, polymericfilms and similar media. However, such equipment is costly and the areasof electro-optic media presently sold may be insufficient to justifydedicated equipment, so that it may typically be necessary to transportthe coated medium from a commercial coating plant to the plant used forfinal assembly of electro-optic displays without damage to therelatively fragile layer of electro-optic medium.

The aforementioned U.S. Pat. No. 6,982,178 describes a method ofassembling a solid electro-optic display (including a particle-basedelectrophoretic display) which is well adapted for mass production.Essentially, this patent describes a so-called “front plane laminate”(“FPL”) which comprises, in order, a light-transmissiveelectrically-conductive layer; a layer of a solid electro-optic mediumin electrical contact with the electrically-conductive layer; anadhesive layer; and a release sheet. Typically, the light-transmissiveelectrically-conductive layer will be carried on a light-transmissivesubstrate, which is preferably flexible, in the sense that the substratecan be manually wrapped around a drum (say) 10 inches (254 mm) indiameter without permanent deformation. The term “light-transmissive” isused in this patent and herein to mean that the layer thus designatedtransmits sufficient light to enable an observer, looking through thatlayer, to observe the change in display states of the electro-opticmedium, which will be normally be viewed through theelectrically-conductive layer and adjacent substrate (if present). Thesubstrate will be typically be a polymeric film, and will normally havea thickness in the range of about 1 to about 25 mil (25 to 634 μm),preferably about 2 to about 10 mil (51 to 254 μm). Theelectrically-conductive layer is conveniently a thin metal layer of, forexample, aluminum or ITO, or may be a conductive polymer. Poly(ethyleneterephthalate) (PET) films coated with aluminum or ITO are availablecommercially, for example as “aluminized Mylar” (“Mylar” is a RegisteredTrade Mark) from E.I. du Pont de Nemours & Company, Wilmington Del., andsuch commercial materials may be used with good results in the frontplane laminate.

Assembly of an electro-optic display using such a front plane laminatemay be effected by removing the release sheet from the front planelaminate and contacting the adhesive layer with the backplane underconditions effective to cause the adhesive layer to adhere to thebackplane, thereby securing the adhesive layer, layer of electro-opticmedium and electrically-conductive layer to the backplane. This processis well-adapted to mass production since the front plane laminate may bemass produced, typically using roll-to-roll coating techniques, and thencut into pieces of any size needed for use with specific backplanes.

The aforementioned U.S. Pat. No. 6,982,178 also describes a method fortesting the electro-optic medium in a front plane laminate prior toincorporation of the front plane laminate into a display. In thistesting method, the release sheet is provided with an electricallyconductive layer, and a voltage sufficient to change the optical stateof the electro-optic medium is applied between this electricallyconductive layer and the electrically conductive layer on the opposedside of the electro-optic medium. Observation of the electro-opticmedium will then reveal any faults in the medium, thus avoidinglaminating faulty electro-optic medium into a display, with theresultant cost of scrapping the entire display, not merely the faultyfront plane laminate.

The aforementioned U.S. Pat. No. 6,982,178 also describes a secondmethod for testing the electro-optic medium in a front plane laminate byplacing an electrostatic charge on the release sheet, thus forming animage on the electro-optic medium. This image is then observed in thesame way as before to detect any faults in the electro-optic medium.

The aforementioned U.S. Pat. No. 7,561,324 describes a so-called “doublerelease film” which is essentially a simplified version of the frontplane laminate of the aforementioned U.S. Pat. No. 6,982,178. One formof the double release sheet comprises a layer of a solid electro-opticmedium sandwiched between two adhesive layers, one or both of theadhesive layers being covered by a release sheet. Another form of thedouble release sheet comprises a layer of a solid electro-optic mediumsandwiched between two release sheets. Both forms of the double releasefilm are intended for use in a process generally similar to the processfor assembling an electro-optic display from a front plane laminatealready described, but involving two separate laminations; typically, ina first lamination the double release sheet is laminated to a frontelectrode to form a front sub-assembly, and then in a second laminationthe front sub-assembly is laminated to a backplane to form the finaldisplay, although the order of these two laminations could be reversedif desired.

The aforementioned U.S. Pat. No. 7,839,564 describes a so-called“inverted front plane laminate”, which is a variant of the front planelaminate described in the aforementioned U.S. Pat. No. 6,982,178. Thisinverted front plane laminate comprises, in order, at least one of alight-transmissive protective layer and a light-transmissiveelectrically-conductive layer; an adhesive layer; a layer of a solidelectro-optic medium; and a release sheet. This inverted front planelaminate is used to form an electro-optic display having a layer oflamination adhesive between the electro-optic layer and the frontelectrode or front substrate; a second, typically thin layer of adhesivemay or may not be present between the electro-optic layer and abackplane. Such electro-optic displays can combine good resolution withgood low temperature performance.

The aforementioned U.S. Pat. No. 7,839,564 also describes variousmethods designed for high volume manufacture of electro-optic displaysusing inverted front plane laminates; preferred forms of these methodsare “multi-up” methods designed to allow lamination of components for aplurality of electro-optic displays at one time.

The aforementioned U.S. Pat. No. 6,982,178 also describes methods forforming an electrical connection between a backplane to which the frontplane laminate is laminated and the light-transmissiveelectrically-conductive layer within the front plane laminate. Asillustrated in FIGS. 21 and 22 of this patent, the formation of thelayer of electro-optic medium within the front plane laminate may becontrolled so as to leave uncoated areas (“gutters”) where noelectro-optic medium is present, and portions of these uncoated areascan later serve to form the necessary electrical connections. However,this method of forming connections tends to be undesirable from amanufacturing point of view, since the placement of the connections isof course a function of the backplane design, so that FPL coated with aspecific arrangement of gutters can only be used with one, or a limitedrange of backplanes, whereas for economic reasons it is desirable toproduce only one form of FPL which can be used with any backplane.

Accordingly, the aforementioned U.S. Pat. No. 6,982,178 also describesmethods for forming the necessary electrical connections by coatingelectro-optic medium over the whole area of the FPL and then removingthe electro-optic medium where it is desired to form electricalconnections. However, such removal of electro-optic medium poses its ownproblems. Typically, the electro-optic medium must be removed by the useof solvents or mechanical cleaning, either of which may result in damageto, or removal of, the electrically-conductive layer of the FPL (thiselectrically-conductive layer usually being a layer of a metal oxide,for example indium tin oxide, less than 1 μm thick), causing a failedelectrical connection. In extreme cases, damage may also be caused tothe front substrate (typically a polymeric film) which is used tosupport and mechanically protect the conductive layer. In some cases,the materials from which the electro-optic medium is formed may not beeasily solvated, and it may not be possible to remove them without theuse of aggressive solvents and/or high mechanical pressures, either ofwhich will exacerbate the aforementioned problems.

Similar methods using selective coating of electro-optic medium and/orselective removal of electro-optic medium may also be applied to thedouble release films and inverted front plane laminates discussed above.

It is common practice to use laser cutting to separate from a continuousweb of FPL pieces of appropriate sizes for lamination to individualbackplanes. Such laser cutting can also be used to prepare areas forelectrical connections to the backplane by “kiss cutting” the FPL withthe laser from the lamination adhesive side so that the laminationadhesive and electro-optic medium are removed from the connection areas,but the electrically-conductive layer is not removed. Such kiss cuttingrequires accurate control of both laser power and cutting speed if thethin and relatively fragile electrically-conductive layer is not to beremoved or damaged. Furthermore, following the kiss cutting it isnormally necessary to mechanically or chemically remove (“clean”) theresidue of the electro-optic and/or adhesive layers from theelectrically-conductive layer in order to enable good electrical contactto be made with this layer. Also, depending upon the location of theconnection, bending of the electrically-conductive layer and theassociated front substrate may crack the conductive layer, resulting infailure to make a proper connection between the backplane and theconductive layer, and hence display failure. In practice, it isnecessary to inspect each FPL piece after the cleaning step is completedand before the FPL piece is laminated to a backplane. Just prior to theFPL/backplane lamination, a small quantity of a conductive adhesive orink is placed on the backplane at the points where the front electrodeconnections will be made. Following the lamination, the conductiveadhesive or ink electrically connects the front electrode to thebackplane. Typically, a protective sheet is them laminated over theviewing surface of the display, followed by an edge sealing operation toproduce the final display module. This process poses scalability, yieldand cost concerns when used for mass production of displays.

The aforementioned U.S. Pat. No. 7,733,554 describes two processes forproviding electrical connections between a front electrode and abackplane without kiss cutting. In the first, so-called “pre-formedconnection aperture” or “PFCA” process, a sub-assembly is first formedcomprising a layer of lamination adhesive and a layer of electro-opticmedium, An aperture is cut through this sub-assembly, and then there issecured to the exposed surface of the layer of lamination adhesive alight-transmissive electrode layer, the electrode layer extending acrossthe aperture. The second, so-called “extended tab” process, starts withformation of the same sub-assembly comprising a layer of laminationadhesive and a layer of electro-optic medium. However, in the extendedtab process, no aperture is formed through the sub-assembly; instead, alight-transmissive electrode layer is secured to the exposed surface ofthe lamination adhesive layer of the sub-assembly, the electrode layerhaving a tab portion which extends beyond the periphery of the layers oflamination adhesive and electro-optic medium. Although these twoprocesses do avoid the need for kiss cutting a front plane laminate,they suffer from other practical disadvantages when used on a productionscale. Both processes require that the location of the front electrodeconnections (via the apertures or the tabs) be known before the frontelectrode is secured to the electro-optic layer; neither process permitslarge scale manufacture (typically by a roll-to-roll process) of a frontplane laminate in a manner which permits to front laminate to bemodified to produce a variety of displays of different sizes, and thusrequiring different front plane connections.

Accordingly, there is thus a need for improved methods of formingelectrical connections to the conductive layers of front planelaminates, and the present invention seeks to provide such improvedmethods.

SUMMARY OF INVENTION

Accordingly, this invention provides a modification of the kiss cuttingprocess described above. The process of the present invention renders akiss cut unnecessary; instead a cut is made completely through the FPLto form an aperture, and a flowable conductive material is thereafterplaced in the aperture to provide contact between the backplane and theconductive layer of the FPL.

Accordingly, the present invention provides a process for the productionof an electro-optic display, the process comprising:

forming a front plane laminate comprising, in order, alight-transmissive electrically-conductive layer, a layer ofelectro-optic material, and a layer of lamination adhesive;

forming an aperture through all three layers of the front planelaminate; and

introducing a flowable, electrically-conductive material into theaperture, the flowable, electrically-conductive material being inelectrical contact with the light-transmissive electrically-conductivelayer and extending through the adhesive layer.

The process of the present invention may hereinafter for convenience becalled the “through cut” process of the invention.

The term “light-transmissive electrically-conductive layer” is usedherein in the same sense as in the aforementioned U.S. Pat. No.6,982,178. This layer should be sufficiently light-transmissive that auser, viewing the display through the light-transmissiveelectrically-conductive layer can see the changes in the electro-opticproperties of the electro-optic layer as the electro-optic layer isswitched.

In the process of the present invention, the front plane laminate maycomprise a release sheet covering the surface of the layer of laminationadhesive remote from the layer of electro-optic material. The aperturemay or may not extend through such a release sheet, but it is usuallymost convenient for the aperture to extend through the release sheet, sothat all layers of the front plane laminate can be cut in the sameoperation. As discussed in the aforementioned U.S. Pat. No. 6,982,178,the release sheet may comprise a conductive layer, which can be used fortesting the electro-optic layer in the manner already described. Thelight-transmissive electrically-conductive layer may be carried on asupport layer; typically, the electrically-conductive layer is part of afront substrate which comprises in addition to theelectrically-conductive layer, a support layer, typically a polymericfilm, which provides mechanical support and protection for what isnormally a relatively fragile electrode layer. The front plane laminatemay comprise two layers of lamination adhesive on opposed sides of thelayer of electro-optic medium, and in such a front plane laminate theaperture will extend through both layers of lamination adhesive.

The formation of the aperture in the process of the present inventionwill typically be effected by laser cutting, and, for reasons discussedin more detail below, will normally be effected from the adhesive layerside of the front plane laminate

The aperture-containing front plane laminate produced in the presentprocess may be used in a manner exactly similar to aperture-containingFPL's produced by mechanical or solvent removal of electro-optic mediumand lamination adhesive, as described in the aforementioned U.S. Pat.No. 6,982,178. Thus, after removal of the release sheet (if present) thelamination adhesive may be laminated to a backplane comprising at leastone electrode, with the flowable conductive material being introducedinto the aperture prior to or during this lamination so as to provide anelectrical connection between the light-transmissiveelectrically-conductive layer and a contact provided on the backplane.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 of the accompanying drawings is a schematic cross-section througha front plane laminate used in the process of the present inventionafter formation of an aperture through this front plane laminate.

FIG. 2 shows the front plane laminate shown in FIG. 1 being laminated toa backplane

DETAILED DESCRIPTION

As indicated above, the present invention provides a process for theproduction of an electro-optic display. This process starts from a frontplane laminate comprising, in order, a light-transmissiveelectrically-conductive layer, a layer of electro-optic material, and alayer of lamination adhesive. An aperture is formed through all threelayers of the front plane laminate; and a flowable,electrically-conductive material, such as a conductive adhesive orconductive ink, is introduced into the aperture, so that the flowablematerial is in electrical contact with the light-transmissiveelectrically-conductive layer and extends through the adhesive layer.

A preferred process of the present invention will now be described inmore detail, though by way of illustration only, with reference to theaccompanying drawings, which are schematic sections through a frontplane laminate (“FPL”—generally designated 100) at two different stageof the process. The accompanying drawings are not to scale; inparticular the thicknesses of the various layer illustrated are variedfor ease of illustration.

As already mentioned, FIG. 1 of the accompanying drawings is a schematiccross-section through the front plane laminate 100 after formation of anaperture therethrough. The FPL 100 comprises a transparent frontsubstrate 102, formed from a poly(ethylene terephthalate) (PET) film, alight-transmissive, electrically-conductive layer 104, which may beformed from indium tin oxide (ITO) or a conductive polymer, a layer ofelectro-optic material 106 (illustrated as an encapsulatedelectrophoretic layer), an adhesive layer 108 and a release sheet 110provided, on its surface facing the adhesive layer 108, with aconductive layer 112, which may conveniently be a thin layer ofaluminum. As illustrated in FIG. 1, an aperture 114 has been cut throughall the layers of the FPL by means of a laser cutter directed at the FPLfrom the release sheet side (i.e., downwardly as illustrated by thearrow in FIG. 1).

As may be seen in FIG. 1, an observer looking downwardly through theaperture 114 through the FPL 100 will seen areas 104a of theelectrically-conductive layer 104 exposed near the bottom of theaperture 114. The aperture cutting process exposes theelectrically-conductive layer 104 electrode in two ways: 1) during thelaser cutting process the PET/ITO film used to form the layers 102 and104 melts, vaporizes and shrinks, thus enlarging the aperture; as thePET shrinks or burns back, the ITO layer 104 is pulled up into thecylinder formed by the cutting process, in a manner similar to that bywhich a plated via is formed during printed circuit board construction;and 2) the electro-optic 106 and lamination adhesive 108 layers areburned back more than the PET/ITO, thus exposing additional ITO layer104.

FIG. 2 shows the FPL 100 shown in FIG. 1 being laminated to a backplane116. (Please note that the FPL in FIG. 2 is inverted relative to itsposition in FIG. 1.) The FPL first has the release sheet 110 and itsattached conductive layer 112 removed. The FPL is then placed adjacentthe backplane 116 with the adhesive layer 108 in contact with thebackplane, and a flowable conductive material 118, preferably aconductive adhesive, is dispensed into the aperture in the FPL. Theflowable conductive material forms a conductive via extending throughthe aperture in the FPL and establishing electrical contact between theconductive layer 104 and an electrode 120 provided on the backplane 116.The FPL and the backplane 116 are then typically passed through alaminator (not shown) and laminated together under heat and pressure.Following this lamination, a protective sheet may be laminated over theFPL and the edges sealed, for example in any of the ways described inthe aforementioned U.S. Pat. No. 6,982,178.

When using the process of the present invention, inspection of the frontplane laminate can take place while the FPL is still in the form oflarge sheets or rolls, in such a way that the subsequently cut FPL isidentifiable as fit for use. Typically, this task is performed using agrid overlay to identify individual FPL within a larger sheet or roll.The desired shape of FPL for a display may be is formed the usual waywith a laser cutter.

The present invention may allow elimination of the prior art requirementfor piece part inspection, kiss cutting, release sheet removal andcleaning of electro-optic and adhesive layers of the FPL during fordisplay manufacture. These process steps could be are replaced byinspection of large sheets or rolls, formation of apertures for frontelectrode connections at the same time that individual pieces of FPL arecut for displays. This could increase throughput and decrease yield lossassociated with cleaning and laser kiss cutting. Additionally, theprocess of the present invention should result in manufacturingprocessing cost and tact time reduction.

This invention may allow for a reduction in size of the FPL tabcurrently used for creating a top plane connection; see for example theaforementioned U.S. Pat. No. 8,034,209. Currently, one limitation on thetop plane connection size is the need for mechanical cleaning bytechnicians. Using the laser to create patterns at the connection sitecould greatly increase the amount of exposed conductive layer for agiven cut area. For example, cutting a series of tightly groupedparallel lines in a 1 mm square offers greater conductive layer exposurethan a circular hole of equal area. The pattern density is a function ofthe laser beam focus, mechanical tolerance of the machine and the meltcharacteristics of the front substrate used to support the conductivelayer.

The amount of conductive layer exposed is easily adjustable and can takeon any shape the laser is capable of cutting, this may be a usefulfeature as the amount of electrode contact required changes with displaysize.

Another technical advantage of this invention is that it may allow theuse of alternative electrode materials that are not top plane cleanableusing the current chemical and mechanical methods. Some alternativeelectrode materials are very sensitive to the current cleaning process,for example poly-3,4-ethylenedioxythiophene (PEDOT), a conductivepolymer which can be used as the conductive layer, is easily damaged bymechanical scrubbing and use of solvents.

The electrode arrangements in the displays produced using the process ofthe present invention can be of any of the types described in theaforementioned E Ink and MIT patents and applications. Thus, forexample, the displays may be of the direct drive type, in which thebackplane is provided with a plurality of electrodes, each of which isprovided with a separate connector by means of which a controller cancontrol the voltage applied to the specific electrode. In such a directdrive display, a single continuous front electrode is usually providedcovering the whole display, although other front electrode arrangementsare possible. Depending upon the type of electro-optic material used, itmay be possible to use a passive matrix drive arrangement in which(typically) the backplane carries a plurality of elongate parallelelectrodes (“column electrodes”), while on the opposed side of theelectro-optic material there is provided a plurality of elongateparallel electrodes (“row electrodes”) running at right angles to thecolumn electrodes, the overlap between one specific column electrode andone specific row electrode defining one pixel of the display. Thepresent displays may also be of the active matrix type, typically with asingle continuous front electrode covering the whole display and amatrix of pixel electrodes on the backplane, each pixel electrodedefining one pixel of the display and having an associated transistor orother non-linear element, the active matrix display being scanned in theconventional manner to write the display in a row-by-row fashion.Finally, the present display may also be of the stylus-driven type, with(typically) a single electrode on the backplane and no permanent frontelectrode, writing of the display being effected by moving a stylusacross the front surface of the display.

The process of the present invention may make use of any of the types ofelectro-optic material discussed above. Thus, for example, theelectro-optic material in the front plane laminate may comprise arotating bichromal member, electrochromic or electro-wetting material.Alternatively, the electro-optic material may comprise anelectrophoretic material comprising a plurality of electrically chargedparticles disposed in a fluid and capable of moving through the fluidunder the influence of an electric field. The electrically chargedparticles and the fluid may be confined within a plurality of capsulesor microcells, or may be present as a plurality of discrete dropletssurrounded by a continuous phase comprising a polymeric material. Thefluid may be liquid or gaseous.

It will be apparent to those skilled in the art that numerous changesand modifications can be made in the specific embodiments of theinvention described above without departing from the scope of theinvention. Accordingly, the whole of the foregoing description is to beinterpreted in an illustrative and not in a limitative sense.

1. A process for the production of an electro-optic display, the processcomprising: forming a front plane laminate comprising, in order, alight-transmissive electrically-conductive layer, a layer ofelectro-optic material, and a layer of lamination adhesive; forming anaperture through all three layers of the front plane laminate; andintroducing a flowable, electrically-conductive material into theaperture, the flowable, electrically-conductive material being inelectrical contact with the light-transmissive electrically-conductivelayer and extending through the adhesive layer.
 2. A process accordingto claim 1 wherein the front plane laminate comprises a release sheetcovering the surface of the layer of lamination adhesive remote from thelayer of electro-optic material.
 3. A process according to claim 2wherein the release sheet comprises a conductive layer.
 4. A processaccording to claim 2 wherein the aperture extends through the releasesheet.
 5. A process according to claim 1 wherein the front planelaminate comprises two layers of lamination adhesive on opposed sides ofthe layer of electro-optic medium, and the aperture extends through bothlayers of lamination adhesive.
 6. A process according to claim 1 whereinthe formation of the aperture is effected by laser cutting.
 7. A processaccording to claim 6 wherein the laser cutting is effected from theadhesive layer side of the front plane laminate.
 8. A process accordingto claim 1 wherein the electrically-conductive material comprises aconductive adhesive or a conductive ink.
 9. A process according to claim2 further comprising removing the release sheet from the front planelaminate; and laminating the remaining layers of the front planelaminate to a backplane comprising at least one electrode, wherein theflowable conductive material is introduced into the aperture prior to orduring the lamination so as to provide an electrical connection betweenthe light-transmissive electrically-conductive layer and a contactprovided on the backplane.
 10. A process according to claim 9 furthercomprising laminating a protective sheet over the front plane laminateafter the front plane laminate has been laminated to the backplane. 11.A process according to claim 1 wherein the electro-optic materialcomprises a rotating bichromal member, electrochromic or electro-wettingmaterial.
 12. A process according to claim 1 wherein the electro-opticmaterial comprises an electrophoretic material comprising a plurality ofelectrically charged particles disposed in a fluid and capable of movingthrough the fluid under the influence of an electric field.
 13. Aprocess according to claim 12 wherein the electrically charged particlesand the fluid are confined within a plurality of capsules or microcells.14. A process according to claim 12 wherein the electrically chargedparticles and the fluid are present as a plurality of discrete dropletssurrounded by a continuous phase comprising a polymeric material.
 15. Aprocess according to claim 12 wherein the fluid is gaseous.